The present invention relates to a cooling system for an engine, said cooling system being divided into an inner circuit and an outer circuit. The inner circuit comprises a radiator, a cooling pump, a thermostat housing, an ejector pump and cooling channels arranged inside the engine. The ejector pump is arranged to draw coolant from the outer system, which comprises an expansion tank, ducting interconnecting the expansion tank and the ejector pump and ducting interconnecting the inner circuit and the expansion tank and deliver it to the inner system.
Moreover, the present invention relates to an ejector pump for pressurizing a cooling system of a combustion engine.
As is well known by persons skilled in the art, the main purpose of a cooling system of an engine is to transfer heat generated in the engine to a radiator, where the heat could be vented to the ambient air. In its simplest form, a cooling system could comprise area-increasing metal fins arranged e.g. on cylinder walls of the engine to be cooled. This type of cooling is generally referred to as air-cooling, and was the first cooling system used on internal combustion engines.
On modern, high performance engines, air-cooling is not sufficient to cool the engine; instead, a cooling system with a coolant is arranged. The coolant is usually water mixed with anti-freezing and anti-corrosion agents and the ducting is arranged to move the coolant from cooling channels in the engine (where the coolant absorbs heat from the engine, hence cooling it) to a radiator, where the absorbed heat is vented to the ambient air. This type of cooling is generally referred to as water-cooling, and is much more efficient than air cooling.
In order to ensure a cooling that is not too great, and not too small, there is usually provided a thermostat in the coolant ducting. The purpose of the thermostat is to redirect coolant to bypass the radiator if the coolant should be cooler than desired.
There are however some problems to be solved relating to water cooling: Firstly, there is a trend towards higher coolant temperatures; a high coolant temperature gives a higher maximum cooling rate (due to a larger temperature difference between the coolant and the ambient air) and also less heat transfer from the engine's combustion chambers to the coolant, which is beneficial for engine efficiency. The higher temperatures lead to higher stress levels on cooling system components made of plastic materials or rubber. Especially the expansion chamber (a component well known by persons skilled in the art) is a component that gets significantly more expensive if it should stand elevated coolant temperatures.
Secondly, water-cooling systems have problems with cavitation; cavitation means that a liquid is forced to boil by decompression, which gives gas bubbles in the liquid; these gas bubbles have, however, a very short life; as soon as the pressure in the liquid returns to normal levels, the bubbles will implode to liquid. Cavitation is detrimental to cooling system components due to the “micro-shocks” resulting from the bubble implosions, and is rather common in cooling systems. The results of cavitation, e.g. small “holes” in metal components constituting the cooling system, could be seen e.g. on pumping fins.
Thirdly, water-cooling systems have problems with boiling after engine shut-off; after the engine has been shut off, the coolant will stop circulating in the cooling system. Remaining heat from e.g. the cylinder walls and the exhaust manifold will be transferred to the coolant, which might reach boiling temperature. As is well known by persons skilled in the art, the volume of gas exceeds the volume of the liquid it emanates from, under normal atmospheric conditions by a factor exceeding 100. The volume increase emanating from boiling might force coolant out from the cooling system, which leads to increased coolant consumption. Fourthly, air entrainment might (or rather, will) pose a problem if the coolant is not deaerated continuously. In prior art system, the deaeration of the coolant will take place in the expansion chamber, but as will be evident in the following, this is a solution that will not be very efficient in the future.
One efficient, known, way of reducing the problems with cavitation and boiling after engine shut-off is to increase the coolant pressure. This is however rather expensive, since the expansion tank must be a vessel standing high pressures, i.e. a vessel having thick walls.
U.S. Pat. No. 4,346,757 describes an automotive vehicle cooling system having a radiator connected to the engine coolant jacket for circulation of coolant, a pump delivering coolant from the radiator to the engine, a non-pressurized reservoir bottle, or expansion vessel, communicating with a radiator and having a make-up line communicating with a Venturi in a recirculating line around the pump directing coolant from the pump outlet to the pump inlet. The Venturi allows make-up coolant to be added from the reservoir bottle at atmospheric pressure so that the bottle can be of a relatively light-weight gauge material.
U.S. Pat. No. 4,346,757 solves, in part, the problem with cavitation by putting the cooling system under pressure; however, deaeration of the coolant takes place in the expansion vessel, which requires a constant stream of coolant from the cooling system to the expansion vessel. At low engine speed, and as the engine is shut off, there will be only a small, or no, pressure increase in the cooling system, since the pressure in the cooling system and the expansion chamber will be equalized rapidly at low engine speeds or as the engine is shut off, due to the provision of a capillary hose (34) between the radiator and the expansion vessel. Consequently, the design according to U.S. Pat. No. 4,346,757 does not in any way address the problem of boiling after engine shut-off.
U.S. Pat. No. 6,886,503 describes a cooling system wherein the internal pressure is increased by letting in compressed air from a turbocharger into the expansion vessel. Although simple and cost efficient, this solution addresses neither the problem of expensive, pressure capable expansion vessels nor coolant boiling after engine shut-off.
One problem with subjecting an expansion vessel for compressed air, is that this type of vessel will “breathe” frequently and coolant can escape from the vessel each time the inlet valve is opened.
It is desirable to provide a cooling system having an elevated pressure, which pressure remains at low engine speed and after engine shut-off.
According to an aspect of the invention, solved by the provision of a one-way valve placed in a ducting interconnecting the expansion tank and an inner cooling circuit.
In order to reach a sufficient working pressure, the one-way valve could have an opening pressure of about 0.5 bar.
If the one-way valve has an opening pressure of about 0.5 bars, a second one-way valve allowing a coolant flow from the expansion tank towards the ejector pump is preferably provided.
In order to obtain an efficient deaeration of the coolant, a deaeration tank could serve as a junction for a ducting from an elevated position in the engine cooling system, a ducting from an inlet of the coolant pump, a ducting from a top portion of the radiator, and the ducting interconnecting the inner circuit and the expansion tank.
The deaeration tank could have a volume of about 1-5 liter.
Furthermore, the ejector pump comprises an inlet chamber connected to an expansion tank, a nozzle opening in the inlet chamber and ejecting a flow of coolant towards a neck connecting the inlet chamber and a mixing zone having an increasing diameter in a flow direction of the coolant flow ejected from the nozzle. In order to get a sufficient pumping effect, the nozzle diameter could be about 2-4 mm and the neck diameter could be about 5-10 mm. The length of the mixing zone could be about 4 to 10 times the diameter of the neck, and the mixing zone 175 could have a diameter increasing from the neck diameter to about 2 to 3 times the diameter of the neck.